14 ' MARGINELLA. 



Persicula, those volutiform species having a depressed or sunken 

 spire. 



Swainson, in 1840, founded a classification upon slight differ- 

 ences in the form of the species ; extremely unsatisfactory because 

 the change of form in the series is gradual. His genera are 

 Volutella, Perxicula, Gibberula and Glabella. 



In 1844, Hinds divided the species into two groups : Phdeno- 

 ptra,with elevated spire ; Cryptoxpira, with hidden spire. The 

 first corresponds with Marginella as restricted by Schumacher, 

 the second with that author's Persicula. . H. and A. Adams, 

 however, have adopted Cryptospira as a subgenus of Marginella, 

 with nearly obsolete spire, and last whorl gibbous posteriorly; 

 following it, they place the genus Persicula, with depressed 

 spire. 



Petit, in 1851, divided Marginella into three sections : 



1. With spire more or less elevated. 



2. With spire depressed or hidden, sometimes umbilicated. 



3. Columbelliform species, connecting with the genus Erato. 



Gray, in 1857, admitted three genera : 1. Porcellana ( Mar- 

 ginella) ; 2. Closia, for M. sarda, and not differing essentially 

 from 3, Persicula. 



Messrs. H. and A. Adams, in their " Genera of Recent Mol- 

 lusca," admit three genera : 



Marginella, with the subgenera Glabella, Prunum, Volutella, 

 and Cryptospira. 



Persicula, with the subgenus Gibberula. 



Volvaria, with the subgenus Volvarina. 



J. H. Redfield, in 1870, writes: "As to the numerous 

 subgenera which have been proposed for species of this genus, 

 they seem to me to be neither useful nor well grounded. In a 

 series of two or three hundred species it is easy to select a few 

 salient forms for subgeneric types, but much less easy to allot 

 all the intermediate species to their proper places under* such 

 types. All the proposed subgenera are founded on the greater 

 or less prominence of the spire, and on the degree of the 

 thickening or reflection of the outer lip. A very slight difference 

 of the plane of development is all that is involved in the former 

 character, and all students of the great family Helicidse under- 

 stand well how little generic value attaches to either character. 



